The increasing use of the internal combustion engine as motive power for passenger cars, busses, trucks, tractors, industrial equipment and the like has resulted in problems of air pollution and fuel shortages. Various expedients are being employed and others are being developed for the reduction of pollutants emitted into the atmosphere. Prior to the application of remedial equipment, approximately 20% of the total quantity of unburned hydrocarbons escaped to the atmosphere from the crankcase of the engine which received blowby gases from the several cylinders. To eliminate this source of pollution, crankcases are being closed to the atmosphere and the crankcase vapors are conducted to the intake manifold for ingestion and combustion in the cylinders.
The system for handling the crankcase vapors, generally referred to as "positive crankcase ventilation", or simply PCV, includes a valve the function of which is to meter the flow of vapors and gases from the crankcase to the intake manifold during various modes of operation of the engine; i.e., idle, acceleration, cruising, deceleration, of a vehicle. The valve plunger floats between a seat at its intake end and a metering arrangement at its outlet end, subject to the forces of a spring urging the plunger toward its seat and the degree of vacuum in the intake manifold. The ordinary PCV valve is completely closed only when the engine is not running. During periods of deceleration and idle, manifold vacuum is relatively high and the plunger is drawn by the vacuum against the force of the spring toward the outlet end of the valve, restricting but not completely stopping the flow of air and crankcase vapors to the intake manifold. During acceleration and constant speed operation, the plunger assumes a mid-position permitting maximum flow of the vapors into the intake manifold.
All positive crankcase ventilation systems permit ventilating air to enter the crankcase and pass, along with crankcase vapors, to the intake manifold during all times that the engine is in operation.
It has been found that while the positive crankcase ventilation system which employs the metering valve as described performs its intended function of continuously withdrawing vapors from the crankcase and conducting them to the engine intake, its use tends to make starting of the engine more difficult, especially in cold weather, cause rough running of the engine and requires relatively frequent attention for proper operation.
The object of the present invention is to provide an improved crankcase ventilation system which in large measure avoids the adverse consequences of use of the standard positive crankcase ventilation system above described. More specifically, the system, while providing for the continuous ventilation of the crankcase, avoids the supplemental supply of air to the intake while starting the engine and permits the flow of relatively large quantities of air to relieve the otherwise excessively high vacuum developed in the intake manifold during deceleration. Thus, a relatively richer mixture of fuel and air is supplied to the cylinders on starting to promote ignition of the cold mixture in the cylinders and air is supplied to prevent the passing through of unburned hydrocarbons to the exhaust during deceleration. A further object of the invention is to improve the ventilation of the crankcases of V-type engines by withdrawing fumes from both sides.
The achievements and advantages of the positive crankcase ventilation system of this invention will become more fully apparent as the description thereof proceeds in conjunction with the accompanying drawings .